Many kinds of footwear, such as athletic shoes, everyday walking shoes, and work boots have the drawback of poor ventilation. Poor ventilation causes a moist, muggy environment in the shoe which can lead to unpleasant foot odor and foot discomfort for the wearer.
There have been various attempts to solve the problem of ventilating a shoe. Many of the approaches have included a bladder encased within the sole of the shoe. Generally, the weight of the foot is used to compress the bladder and force air out of apertures to ventilate the foot.
However, several problems exist with the prior art attempts to solve the ventilation problem using a bladder. Prior art devices have typically placed the bladder in the center of the heel portion of the sole. As a result, the bladder deflates very easily, causing the shoe to lose its shock-absorbing properties. This results in loss of heel cushion and, therefore, wearer discomfort.
Problems have also existed with failure of the bladder to reinflate. The shape and position of the bladder, or air pump, has been such that enough weight is always on it to prevent full inflation. This results in inefficient operation of the pump.
Most of the prior art devices are sufficiently built into the shoe so that they are not easily replaceable. Thus, should the ventilating capability of the shoe wear out, the user would have to either replace the whole shoe or tolerate poor ventilation.
The intake venting of many prior art devices leads out to the side of the shoe. This could cause water to be sucked into the inside of the shoe. Although such a design is not a serious problem in an athletic shoe, it would prove disastrous in a work or hunting shoe.
Finally, the prior art devices do not take into account the physiology of the foot during walking. Foot physiology is critical to determining bladder shape and placement for optimum ventilation.
The physiology of the human foot and the biomechanics of how it functions during walking make the motion of the foot within a shoe very predictable. The foot basically makes an "S" pattern during walking. At the beginning of each step the foot strikes the ground on the outside edge of the heel. A lateral line drawn across the base of the heel would be about a five to ten degree angle relative to the walking surface.
The second phase is called pronation. This occurs when the weight bearing part of the foot transfers through a rolling motion, from the outside or lateral edge of the calcaneus across to the medial or inside portion of the ankle at the base of the tibia, and rests very briefly on the medial longitudinal arch. The weight at this point is resting on an arched structure whose points of contact are the first metatarsal head and the calcaneus. At this point, the flesh around the perimeter of the heel is displaced laterally from the calcaneus.
The weight then shifts back across the foot in the supination phase. The load is transferred across the tops of the metatarsal bones and back through the ankle structure to rest on the lateral arch created by the arc of the fifth metatarsal bone from the head to the cuboid bone. Where the pronation phase is sometimes called "rolling in," this phase can be referred to as "rolling out."
After the foot has progressed from the heel strike through the pronation and supination phases it finally ends with the push off. The weight is transferred back across the foot through the metatarsal arch. Finally, the phalange and sesamoids of the big or first toe and the phalanges of the second toe propel the person forward.
What has been needed is a simple, low cost insole for ventilating a shoe which: incorporates a bladder designed to reinflate between heel compressions; maintains heel cushion and wearer comfort; is easily replaceable; prevents moisture from being drawn into the shoe; and takes into account the physiology of the foot during walking to optimize ventilation.